The use of polymeric film bases to carry photographic layers is well known. In particular, photographic elements which require accurate physical characteristics use polyester film bases, such as polyethylene terephthalate and polyethylene naphthalate film bases. In fact, polyester film bases, when compared with commonly used cellulose ester film bases, are dimensionally more stable and more resistant to mechanical stresses under most conditions of use.
The formation of static electric charges on film bases is a serious problem in the production and use of photographic elements. While coating the light-sensitive photographic emulsion, electric charges accumulate on the base discharge, producing light which may be recorded as an image on the light-sensitive layer. Other drawbacks which result from the accumulation of electric charges on polymeric film bases are the adherence of dust and dirt, and the creation of coating defects.
Additionally, photographic elements comprising light-sensitive layers coated onto polymeric film bases, when used in rolls or reels which are mechanically wound and unwound or in sheets which are conveyed at high speed, tend to accumulate static charges and record the light generated by static discharges.
The static-related damages may occur not only before the photographic element has been manufactured, exposed and processed, but also after processing when the photographic element including the image is used with other photosensitive media to reproduce or enlarge the image. Accordingly, it is desired to provide permanent antistatic protection, that is antistatic protection which retains its effectiveness even after photographic processing.
Several techniques have been suggested to protect photographic elements from the adverse effects of static charges.
Matting agents, hygroscopic materials or electroconductive polymers have been proposed to prevent static buildup, each acting with a different mechanism. However, matting agents cause haze, dust and dirt problems; hygroscopic materials cause sheets or films to stick together or to other surfaces; and electroconductive polymers are not permanent after photographic processing or may not be transparent when coated with conventional binders.
U.S. Pat. No. 4,225,665 purports to disclose permanent antistatic layers for photographic elements. These layers consist essentially of three components: (1) a water-soluble, electrically conductive polymer comprising carboxylic groups, (2) a hydrophobic polymeric binder containing carboxylic groups, and (3) a polyfunctional aziridine crosslinking agent. This composition, however, tends to give hazy coatings and allows premature reactions among the components prior to coating. U.S. Pat. No. 4,701,403 suggests a costly system of coating the components as two separate coatings to avoid these premature reactions.
U.S. Pat. No. 4,585,730 discloses a photographic element comprising a film base, a silver halide emulsion on one side of the support, and an antistatic layer on the other side of said support, wherein the antistatic layer is coated with an auxiliary gelatin layer containing a conductive polymer, whereby the antistatic properties of the antistatic layer are conducted through said auxiliary layer. Reference is made to U.S. Pat. No. 4,225,665 and 4,701,403 as useful antistatic layers to be coated with the auxiliary layer according to U.S. Pat. No. 4,585,730. This two layer construction, however, often suffers from poor adhesion between the two layers during photographic processing.
An antistatic layer coated onto a polymeric film base has been described in EP 486,982 and EP 589,329. That antistatic layer comprises the reaction product of a copolymer of sodium polystyrene sulfonate and maleic acid with a polyfunctional epoxide crosslinking agent. This antistatic layer provides good adhesion of photographic gelatin layers coated over it, even during photographic processing. A problem with this antistatic layer relates to its low crosslinking rate, which requires both drying and curing at high temperature to obtain a water resistant permanent antistatic layer.
Arita et al. in U.S. Pat. No. 5,300,602 describe a water soluble polymer containing oxazoline groups useful as crosslinking agent for aqueous resins. The use of this polymer in antistatic composition to be coated on a photographic support base is neither disclosed nor suggested.